George Shirakawa Jr., the embattled Santa Clara County supervisor who was charged Friday with 12 counts of criminal activity, including perjury and misappropriation of funds, resigned from his seat.

In a one-page memo, Shirakawa blamed his woes on depression and gambling. He said he will plead guilty to the charges on March 18.

"For years, I have suffered from depression and a gambling addiction,'' he wrote. "Unfortunately, my gambling addiction went untreated for too long, which led to bad decisions and actions that I deeply regret.''

Shirakawa went on to say he has been in ongoing medical treatment for both afflictions.

While he acknowledged that addictive behavior is not an excuse for his conduct, "there is only one person responsible for my conduct and that person is me.''

"It has been through the treatment process that I realize that I need to accept responsibility for all of my actions. That starts today,'' he wrote.

Shirakawa added that his resignation means the community that has "nurtured and raised me for 50 years and elected me for 20'' can now move forward and focus on more important issues, including public health and safety issues.

He said he will always be grateful for the "immense ongoing support from my community,'' and apologized for his actions.

"To all my constituents,'' he wrote, "I am truly sorry for my actions and for any pain I have caused you.''